Successful corn growth requires sunny days with warm day and nighttime temperatures. Several days of 85-degree highs followed by 70-degree nights are ideal.
Unfortunately, most of Illinois has not consistently experienced these conditions for more than three days in a row. Rather, some areas reached the 90-degree mark recently followed shortly by nighttime temperatures in the upper 30s.
As a result, the corn plant is confused. Thus, growing conditions right now are ideal for corn injury from both pre-emergence and post-emergence herbicide applications.
Most corn herbicides require metabolism, or deactivation, of the herbicides for successful crop safety (exceptions include glyphosate on Roundup Ready corn and glufosinate on Liberty Link corn).
Metabolism is a plant’s ability to deactivate “foreign substances” within the plant itself. This includes viruses, pathogens, and pesticides.
Metabolism is accomplished in plants via a complex chemical process involving mixed function oxidases (MFOs). In a nutshell, MFOs are similar to our own white blood cells -- which fight off foreign substances in our body.
This is why cancer patients have their white blood cell count monitored, as chemotherapy reduces white blood cells, resulting in the body being more susceptible to such things as pathogens and viruses.
The same is true with plants. A plant that is under stress (too cold, too wet, too dry) will have a reduction in MFO production. This reduction in MFO production can result in an overload of herbicide molecules to the site of action, ultimately resulting in crop injury or death. Currently, many of Illinois’s corn acres are undergoing a tremendous amount of stress, which suggests that crop injury may occur.
Listed below are a few recommendations to reduce the potential for corn herbicide injury:
- If a corn residual herbicide has already been applied, be patient. A few days of consistently warmer nighttime temperatures will increase the plant’s ability to metabolize the herbicide.
- If residual herbicides have not yet been applied, consider delaying the application a few days. Once the corn plant returns to its green, lush color, applications should be safer to the corn plant.
- If post-emergence herbicides are needed now, consider waiting a few days (see above). At the very least, avoid aggressive adjuvants in the application.
For more information on herbicide metabolism or the best time apply to apply herbicides to avoid crop injury, contact your local FS crop specialist.
Barry Nash is GROWMARK’s weed science technical manager. His e-mail address is firstname.lastname@example.org